1. Field of the Invention
The present invention relates to antimicrobial compositions for coating medical devices. These compositions are used in methods designed to inhibit the growth of microorganisms and/or the formation of biofilms on the surfaces of such devices.
2. Description of Related Art
Infectious microorganisms such as bacteria, fungi and the like are capable of growing on a wide variety of living and non-living surfaces, including skin, teeth, mucosa, vascular tissue and medical devices including those implanted in-vivo. Individual microorganisms not attached to or growing on a surface are typically referred to as “planktonic”. Planktonic organisms are responsible for a variety of localized and disseminated infections. When planktonic microorganisms grow and disseminate on non-living surfaces such as the surfaces of medical implants, they may cause contamination and biofouling of that surface. In many cases a microorganism can grow and accumulate on a surface to the point of becoming almost impossible to remove. This accumulation takes place through the formation of biofilms. A biofilm typically occurs when one or more microorganisms attach to a surface and secrete a hydrated polymeric matrix that surrounds them. Microorganisms existing in a biofilm, termed sessile, grow in a protected environment that insulates them from attack from antimicrobial agents. These sessile communities can give rise to nonsessile planktonic organisms, which rapidly multiply and disperse.
While planktonic organisms are typically killed by conventional antimicrobial treatments, these conventional treatments often fail to eradicate sessile communities rooted in biofilms. This is presumably due to the fact that the slime coat generated by the sessile film physically protects the underlying organisms by limiting diffusion to the organisms and often by chemical de-activation of the bacteriological agent. For this reason, biofilms are understood to be a frequently occurring reservoir for infectious agents and pose tremendous problems for the health-care industry. The biology of biofilms is described in more detail in Bacterial biofilms: a common cause of persistent infection” J. Costerson, P. Steward, E. Greenberg, Science 284: 1318-1322 (1999).
As noted above, infections associated with implanted medical devices typically involve biofilms, where the sessile community of the biofilm provides a reservoir for an invasive infection. Antibodies and other host immune defenses can be relatively ineffective in killing the organisms contained in a biofilm even though these organisms have elicited the antibody and related immune response. In addition, while antibiotics typically treat infections caused by the planktonic organisms, they are significantly less effective at killing the sessile organisms protected in the biofilm. Consequently, once a biofilm is established on an implant such as a medical device, it can be extremely difficult to treat the infection without actually removing and replacing the device. Unfortunately, even if the contaminated medical device is removed from the host, any replacement device will be particularly susceptible to contamination from the residual microorganisms in the area from which the medical device was removed.
As the difficulties associated with eliminating biofilm-based infections and contamination are well-recognized, a number of technologies have developed to prevent or impair microbial growth on the surface of medical devices. Unfortunately, microbial colonization of medical device surfaces continues to be a significant problem within the health care industry, in part due to ongoing difficulties in the ability to prevent organisms from establishing biofilms on the surfaces of medical devices. Consequently, there is a need in the art for methods and compositions that are effective in inhibiting the microbial growth on the surfaces of the wide variety of medical devices that are susceptible to microbial colonization and biofilm formation.